Emulating SQL LIKE in JavaScript

Question

How can I emulate the SQL keyword LIKE in JavaScript?

For those of you who don\'t know what LIKE is, it\'s a very simple regex which only s

Answer 1

An old question but there are actually no good answers here. TSQL LIKE expressions can contain square-bracket escaped sections that are already almost valid regular expressions and allow for matching % and _. E.g.:

'75%' LIKE '75[%]'
'[foo]' LIKE '[[]foo]' -- ugh

Here's my function to convert a LIKE expression into a RegExp. The input is split into square-bracket and non-square-bracket sections. The square-bracket sections just need backslash escaping and the non-square-bracket sections are fully escaped while the % and _ directives are converted to regular expressions.

const likeRegExp = (expression, caseSensitive = false) =>
    new RegExp(`^${
        expression.split(/(\[.+?\])/g)
        .map((s, i) => i % 2 ?
            s.replace(/\\/g, '\\\\') :
            s.replace(/[-\/\\^$*+?.()|[\]{}%_]/g, m => {
                switch(m) {
                    case '%': return '.*';
                    case '_': return '.';
                    default: return `\\${m}`;
                }
            })
        ).join('')
    }$`, caseSensitive ? '' : 'i');

Answer 2

Here's a function I use, based on PHP's preg_quote function:

function regex_quote(str) {
  return str.replace(new RegExp("([\\.\\\\\\+\\*\\?\\[\\^\\]\\$\\(\\)\\{\\}\\=\\!\\<\\>\\|\\:\\-])", "g"), "\\$1");
}

So your line would now be:

var match = new RegEx(regex_quote(likeExpr).replace("%", ".*").replace("_", ".")).exec(str) != null;

Answer 3

If you want to use a regex, you can wrap each character of the string in square-brackets. Then you only have a few characters to escape.

But a better option might be to truncate the target strings so the length matches your search string and check for equality.